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Popper’s Response to Kuhn

In my last post I reviewed Kuhn’s ideas on how the growth of scientific knowledge takes place. I found that, contrary to popular belief, Kuhn and Popper have more in common than they have different. Both deny all the popular notions of science as being based primarily around use of observation to refute the current theory. Both also deny that scientists are ‘objective’ in the usual sense. Both also agree that this lack of ‘objectivity’ is a good thing for the community as a whole.

What I did not have space for, in my last post, was to give some of Popper’s responses to Kuhn.

Unfortunately, Popper initially misunderstood Kuhn. His initial impressions were more like the popular portrayal of Kuhn as someone that did not believe in the growth of scientific knowledge at all. However, Popper – being Popper – eventually came to accept that he had probably misunderstood Kuhn. (See Myth of the Framework, p. 63, note 19)

However, even with some misunderstandings in mind, Popper’s responses to Kuhn are enlightening.

One of Kuhn’s key points is that it’s difficult to compare two scientific paradigms and that they are never “cumulative” in nature. That is to say, contrary to popular belief, science revolution does not only add to the body of knowledge, but also destroys some of what the old paradigm had. Often, something is lost in the process. Therefore, there is (according to Kuhn) no clear cut criteria for how you determine that one paradigm is better than the other. It is therefore, at least in part, a somewhat subjective process.

Kuhn calls this problem incommensurability: the followers of two competing scientific paradigms will often not accept the same set of assumptions (as do two scientists within a paradigm) and therefore must somewhat talk past each other.

Here is one of the key complaints against Kuhn from Popperians: in fact scientific paradigms are not incommensurable in any total sense.

…we must demand of any better theory, that is, of any theory which may be regarded as progressing beyond some less good theory, that it can be compared with the latter. In other words, that that two theories are not ‘incommensurable’, to use a now fashionable term, introduced in this context by Thomas Kuhn.

For example, Ptolemyt’s astronomy is far from incommensurable with that of Aristarchus and Copernicus. …we can compare the two systems logically. … For example, we may point out the colossal velocities that the rotating sphere of the fixed stars [in Ptolemy’s geo-centric view] must give to the stars that are near to it’s equator, where the rotation of the earth, which in Copernicus’ system replaces that of the fixed stars, involves very much smaller velocities. (Myth of the Framework, p. 54)

Since Popper does not accept total incommensurability, it should not surprise us that Popper see scientific growth as a conservative growth of knowledge.

…progress in science, although revolutionary rather than merely cumulative, is in a certain sense always conservative: a new theory, however revolutionary, must always be able to explain fully the success of its predecessor. In all those cases in which its predecessor was successful, it must yield results at least as good as those of its predecessor… (Myth of the Framework, p. 12)

Here Popper does not deny that Kuhn’s basic premise of ‘scientific revolution’ is incorrect, but rather points out that maybe this wording leads us to certain truths while misleading us from others. Popper, thus, believes that we do in fact have “something like a criterion for judging the quality of a theory compared with its predecessor, and therefore a criterion of progress.” (Myth of the Framework, p. 12)

Yet Popper’s response, while at least pointing out the limits of Kuhn’s “incommensurability,” does not equate to a refutation of Kuhn; for Kuhn does not in fact deny the existence of scientific progress, he simply sees it in a different light.

Falsification vs. Verification – Scientific Realism vs. Positivism

There are other points about Popper that deserve further defense. For one thing, in my last post I quoted Kuhn as saying that Popper’s denial of ‘verification’ is incorrect. However, here I think Kuhn, while right, is missing the point. Kuhn is correct that the only sort of refutation that makes sense in science is that of comparison between two (or more) alternatives. In other words, when dealing with theories, science is comparisons between two (or more) paradigms.

Consider that the existence of knowledge that nothing can travel faster than light did not – and should not – cause scientists to abandon Newtonian physics as their accepted paradigm. How could such a fact cause refutation by itself? Until Einstein proposed Relativity, there was nothing else to accept in the place of Newtonian physics. So only a full counter theory could therefore overthrow the old theory. A failure for a theory to match observation is never enough to overthrow a theory.

I do not see Popper denying this fact. Kuhn has discovered an explanation gap in Popperian epistemology. So clearly Kuhn is right that verification and falsification are one and the same because we only compare competing theories, right?

Well, not exactly. Popper’s emphasis on falsification over verification makes perfect sense within an epistemology based on scientific realism. Popper’s main concern is not that there is no sense in which we can ‘verify’ theories. Clearly, if we are talking about comparing two (or more) theories, we can certainly verify that one of them is the more correct. This is even true for Popper’s epistemology. What we cannot do is verify that there will never be a better theory. That is to say, we can never verify that a theory is one and the same as absolute reality.

But as I hinted in my last post, Kuhn does not believe that such an absolute reality exists:

We are all deeply accustomed to seeing science as the one enterprise that draws constantly nearer to some goal set by nature in advance. But need there be any such goal? Can we not account for both science’s existence and its success in terms of evolution from the community’s state of knowledge at any given time? [See last post.] Does it really help to imagine that there is some one full, objective, true account of nature and that the proper measures of scientific achievement is the extent to which it brings us closer to that ultimate goal? If we can learn to substitute evolution-from-what-we-do-know for evolution-towards-what-we-wish-to-know, a number of vexing problems may vanish in the process. (The Structure of Scientific Revolutions, p. 171)

Since Kuhn, being essentially a Positivist (or what we’ve define as a Positivist so far, anyhow), denies the need to accept even the existence of an absolute reality, it is not surprising that he sees less value in calling the theory comparison inherent in revolutions “falsification.” But Popper, being a Scientific Realist, would not want to call the growth of scientific knowledge “conjecture and verification” because this leaves the impression that one can prove a scientific theory – when in fact this is not possible. All we can really do is refute (or falsify) lesser theories as not being as good and as accurate to reality as the new one.

So here again, we find that the real difference between Kuhn and Popper is really Scientific Realism vs. Positivism. It is difficult to find much else different between them that can’t be explained as differences in wording and semantics. But this one difference is, I will argue, significant.